A conventional anti-vibration device for preventing the vibration generated at the unsprung side of the vehicle from being transmitted to the cabin has, for example, liquid sealed inside the device, as disclosed in Patent Document 1.
As schematically shown in the longitudinal-sectional perspective view of FIG. 10, the liquid-sealed-type anti-vibration device disclosed in Patent Document 1 comprises an inner-tube member 102; an outer-tube member 103 disposed coaxially with the inner-tube member 102 so as to relatively displace in an axial direction with respect to the inner-tube member 102 as vibration is input to the device; a pair of rubber bodies 104a and 104b for connecting the ends of the outer-tube member 103 to the outer circumferential surface of the inner-tube member 102 in a liquid-tight manner; and a fluid chamber 105 configured in such a way that the space defined by the pair of rubber bodies 104a, 104b is sealingly filled with non-compressible liquid. The intermediate section of the inner-tube member 102 in its longitudinal direction is provided with an inner-tube rigid protrusion 106 extending along the entire circumference of the inner-tube member 102. The inner-tube rigid protrusion 106 protrudes toward the outer-tube member 103 and is rubber lined. A rubber partition 108 is provided so as to connect the outer circumferential surface of the inner-tube rigid protrusion 106 and the inner circumferential surface of the outer-tube member 103 in a liquid-tight manner and to partition the fluid chamber 105 into two liquid chambers 107a, 107b. The inner-tube rigid protrusion 106 is provided with a limiting passage 109 for communicating the liquid chambers 107a, 107b with each other.
According to the liquid-sealed-type anti-vibration device 101, it is possible to damp the vibration input by the member on the vibration-generating side and isolate the vibration from the member on the vibration-transmitted side, by means of the liquid column resonance inside the passage generated as the liquid inside the liquid chambers 107a, 107b flows through the limiting passage 109, the flow resistance of the liquid flowing through the limiting passage, and the deformation of the elastic members and the like.
Normally, in such a liquid-sealed-type anti-vibration device 101, in order to achieve sufficient damping performance, more liquid flow through the limiting passage 109 is needed. For this reason, the liquid-sealed-type anti-vibration device 101 disclosed in Patent Document 1 is further configured in such a way that the axial end sections of the outer-tube member 103 are provided with ring-shaped outer-tube rigid protrusions 111a, 111b, which protrude from the inner circumferential surface of the outer-tube member 103 toward the inner-tube member 102; and the rubber bodies 104a, 104b are fixed to the inner circumferential surfaces of the outer-tube rigid protrusions 111a, 111b. In response to the input of vibration, for example, the inner-tube rigid protrusion 106, which displaces upward and downward in conjunction with the inner-tube member 102, moves closer to and away from these outer-tube rigid protrusions 111a, 111b. Accordingly, the liquid chambers 107a, 107b may be effectively compressed or expanded upward or downward by the forces exerted on the radially inner and outer sides of the liquid chambers 107a, 107b, thereby increasing the volume change of the liquid chambers 107a and 107b in response to the input of vibration and hence enhancing the damping performance of the device.
However, in the liquid-sealed-type anti-vibration device 101, since the rubber bodies 104a, 104b are fixed to the inner circumferential surfaces of the outer-tube rigid protrusions 111a and 111b, the radial thicknesses of the rubber bodies 104a, 104b are shortened by the radially protruding lengths of the outer-tube rigid protrusions 111a and 111b. Accordingly, there is a drawback that, when a large impact force is input by the member on the vibration-generating side such that the relative displacement of the inner-tube member 102 and the outer-tube member 103 in the axial direction is particularly large for example, the rubber bodies 104a, 104b are subjected to extreme shear deformation, and thereby the rubber fatigue quickly progresses.
Since the sectional areas of the rubber bodies 104a, 104b in the section including the central axis are small, the rubber bodies 104a, 104b are not capable of withstanding the shear deformation. Accordingly, the fixing surfaces between the outer-tube rigid protrusions 111a, 111b and the rubber bodies 104a, 104b are prone to experiencing concentration of stress, and hence separation.
If the rubber bodies 104a, 104b experience fatigue breakage and the like, the vibration at the unsprung side of the vehicle is directly transmitted to the cabin, thereby decreasing the passenger comfort, and in addition, the vibration adversely affects other devices in the vehicle, thereby inducing secondary failures and potentially causing a severe vehicle malfunction or accident.
Accordingly, in such a liquid-sealed-type anti-vibration device, excellent damping performance as well as excellent durability are required, however, the technology disclosed in Patent Document 1 is not sufficient. Further consideration is needed to prevent particularly the fatigue breakage of the rubber bodies.
In this regard, for example, Patent Document 2 discloses a technology in which a damping plate is provided radially outward of an inner-tube seal member such that upward and downward displacement of the damping plate creates flow of high viscous liquid, thereby achieving damping by means of the shear resistance of the high viscous liquid. In a case where improved damping performance at a certain frequency range is desired, it is sometimes preferable to use low viscous liquid, however, in such a case, sufficient damping performance cannot be achieved by the aforementioned damping plate. Accordingly, the technology disclosed in Patent Document 2 is not highly adaptable to the vibration at frequencies outside of the certain frequency range.
For example, Patent Documents 3 and 4 disclose technologies in which a protruding portion having a limiting passage (orifice passage) therein is formed on an outer-tube member, thereby achieving damping performance by means of the flow resistance of the liquid flowing through the limiting passage. However, in these technologies, since the protruding portion does not move with the upward and downward displacement of an inner-tube member, it is not possible to achieve large volume change of liquid chambers by the upward and downward displacement of the protruding portion.